First Watt SIT-3 proper speaker matches

I have a SIT-3. I understand that it mates best with 4 ohm loads. I’m trying to find out if the amplifier is compatible with some 8 ohm loads. I am considering the Focal Kanta speakers that are 8 ohms and dip down to 4. The Focal Sopra 1 have been reviewed well with a 12w Valvet singled end solid state. I know there are other factors aside from impedance and efficiency but I’m not clear on the topic.

I suggest you look more closely at the specs on the 3M TM, which I own, that sensitivity spec is only applicable above 200 hz.  So you will get plenty of volume in the mid-range and above with low powered tube or SS amps but anemic bass output. I've tried it.
FWIW, Jeff Dorgay at Toneaudio said he was "hypnotized by the mixture of drive, clarity, and sheer space that [the SIT-3] delivers", driving the Sopra No. 3's.  Also said it was "the cleanest window to music" he's ever experienced.

My friend Ron who owns a large variety of mostly vintage Hi End equipment has recently bought a SIT-3 and to date after trying multiple combinations at home remains unimpressed.He brought it around to my place and we tried it with my home built very similar to Living Voice OBX loudspeakers and we both thought the sound was glorious and I thought slightly superior to my Pass Aleph O,s and at least the equal of the VAC 70/70,s although I did have to use more input gain than with either to achieve decent volumes.I am on the lookout for another Aleph O,s to Bi Amp and although the SIT-3 provided beautiful sound my plans have not changed.I am not sure considering the amount of changes I have made through the years that despite its obvious affinity for the Living Voice loudspeakers that I would be willing to spend that much money on an amp that locks you into a limited amount of future speaker choices.
This situation is similar to how Maggie lovers often claim that less than ideal tube amps are wonderful with the speakers. The OP should know that the matchup of the SIT-3 and the speakers will work. Is it the optimum, probably not. 

Nevertheless, the bugaboo is that even if you got a different amp that was supposedly "better" for the speakers, there is NO guarantee you will actually enjoy it more! Actual comparison is a must in these matters. I urge you not to dispose of the First Watt amps before you make a change. 

I ran First Watt J2 (pair) amps to drive the Kingsound King III speakers (ESL) and although not ideal, it was among the best sounds holistically of all amps I had used with the speakers. Just because the match is not perfect in no way means you are assured a more acceptable outcome simply because of trying to match up with a more ideal amp. It's just not that simple.